import java.util.Scanner;

public class lq3 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int r=sc.nextInt();
        double PI=3.14159265358979323;
        double s=PI*r*r;
        System.out.println(String.format("%.7f",s));
        sc.close();
    }
}
